1. Technical Field
The present invention relates to a fuel gas supply system and method of a vessel, such as an LNG carrier, and more particularly, to a fuel gas supply system and method of an LNG carrier for efficiently supplying fuel gas from an LNG storage tank to a high-pressure gas injection engine in the LNG carrier.
2. Description of the Related Art
Generally, natural gas is turned into a liquefied natural gas (hereinafter called “LNG”) at a cryogenic temperature in a liquefaction plant, and then transported over long distances to a destination by an LNG carrier.
As liquefaction of natural gas occurs at a cryogenic temperature of −163 degrees Celsius at ambient pressure, LNG is likely to be vaporized even when the temperature of the LNG is slightly higher than −163 degrees Celsius at ambient pressure. In an LNG carrier having an LNG storage tank which is thermally-insulated, as heat is continually transmitted from the outside to the LNG in the LNG storage tank, the LNG is continually vaporized and boil-off gas is generated in the LNG storage tank during the transportation of LNG by the LNG carrier.
In an LNG carrier, if boil-off gas is accumulated in an LNG storage tank, the pressure in the LNG storage tank excessively increases. Consequently, to treat the boil-off gas generated in the LNG storage tank, the boil-off gas is used as a fuel for a ship propulsion engine or burned in a gas combustor.
In case where a high-pressure gas injection engine, for example, MEGI engine manufactured by MAN B&W Diesel Inc., is used as a ship propulsion engine of an LNG carrier, a multi-stage compressor is used in a conventional fuel gas supply system to compress boil-off gas at a high pressure. This multi-stage compression has problems that the fuel gas supply system becomes very complex, and that an excessive amount of power is required to compress the boil-off gas in a gaseous state at a high pressure.